docs: def __add_text(self, text):
          """Adds the given Unicode text as a locally defined symbol."""
          if text is not None and not isinstance(text, six.text_type):
              raise TypeError('Local symbol definition must be a Unicode sequence or None: %r' % text)
          sid = self.__new_sid()
          location = None
          if self.table_type.is_shared:
              location = self.__import_location(sid)
          token = SymbolToken(text, sid, location)
          self.__add(token)
          return token